Two types of glass sealants are currently used in the insulated glass sealant market. One type is a two-component chemically-cured sealant. These sealants are based on polymers such as polyurethanes, polysulfides, mercaptan-modified polyether polyurethanes, and two-component silicones. The other type is a non-curing single-component sealant which is applied to a surface at high temperatures. These sealants are usually butyl rubber-based.
Two-component sealants generally demonstrate superior performance in fully assembled windows. After application, they cure irreversibly to form solid thermoset elastomeric sealants. As a result of the curing process, two-component sealants exhibit good retention of elastomeric properties at elevated temperatures (above 160.degree. F.) and good elastic recovery. Also, due to their inherent formulation ingredients, two-component sealants exhibit good low temperature flexibility at temperatures as low as -40.degree. F. Two-component sealants are generally formulated with organo silane adhesion promoters which function as coupling agents between the sealant and glass substrates. The resulting chemical bond enables the sealant to withstand water immersion and low temperature exposure. The use of two-component sealants as edge sealants in insulated glass applications requires that the sealant have a low moisture vapor transmission rate to improve the sealant's performance. Two-component polyurethane sealants based on hydroxy-terminated polybutadiene are considered to have the lowest moisture vapor transmission rate.
However, two-component sealants have application limitations and disadvantages related to their two-part nature. In using these sealants, both the ratio of components and their mixing is important and must be precise. If there is any error in the ratio of the components, or if improper mixing occurs, the sealant will not cure properly and/or will not adequately chemically adhere to a substrate. Also, two-component sealants have limited work-life and cure times. Once the components of the sealant are mixed they begin to react to form a thermoset crosslinked structure. The reaction is irreversible and cannot be terminated. This creates problems if the reaction occurs too rapidly while the sealant is being applied or if curing occurs during any equipment shutdowns. During equipment shutdowns, the equipment must be thoroughly purged of mixed sealant or the sealant will cure in the equipment. Purging wastes materials and time, thus adding costs to the final product. Further, if the sealant has not properly cured, it is paste-like and if applied to a window in this form it does not have the mechanical properties to sufficiently hold the window together. Any premature handling or movement of the window causes premature cohesive failure of the sealant, and/or sealant-to-substrate bond delamination. Also, slow curing of the sealant requires that the window manufacturing facilities have staging areas to allow the sealant to properly cure. This lost time and space results in higher costs.
Further disadvantages of two-component sealants are that their use in window manufacture cannot be automated easily since they cure slowly and are only paste-like immediately after application. Also, the moisture-vapor transmission rates of two-component sealants are not sufficient for single-seal window applications. To maintain low moisture vapor transmission through an edge seal, a polyisobutylene rubber secondary seal is generally used making the manufacturing processes more complex, resulting in added costs.
Single-component sealants applied at high temperatures generally have better properties at the point of sealant application, as compared to two-component sealants. Mixing of two-components is not required in using a single-component sealant, therefore there is no waste associated with purged materials as in two-component sealants. Also, staging areas are not required as in slow cure two-component sealants. Further, window units can be handled and moved immediately after manufacture. The window manufacturing process using single-component sealants can be easily automated. Also, current linear extruder application technology requires the use of single-component sealants applied at high temperatures. Most single-component sealants are butyl rubber-based, and thus exhibit an inherent low moisture vapor transmission rate which allows the sealants to be used as a single seal. Windows using a single-edge sealant are less complex to manufacture and require fewer materials, resulting in reduced costs.
However, single-component, hot melt edge sealants have disadvantages related to lower performance properties. They are non-curing, and thus do not perform well under high temperature static loads. Their solid elastomeric properties at room temperature always can revert back to a liquid state upon heating. Also, they are generally rubber-based and do not chemically adhere to glass substrates which creates various problems. In order to develop the mechanical bond between a single component sealant and a glass substrate, tensile properties are reduced. Butyl based sealants need to quickly yield in tension in order to maintain their bond to glass. High tensile strength sealants would pull themselves off the glass. Due to this quick yielding property requirement, hot melt single-component sealants often have poor elastic recovery and static load resistance. Also, single-component sealants do not cure and do not chemically bond to glass, so that the mechanical bond can be adversely affected by low temperatures and water at the bond interface. Further, many butyl rubber-based sealants have poor low temperature flexibility further limiting their use in low temperature climates.
International Patent Application, Publication No. WO 97/15619 discloses a one-component, hot-applied, chemically-curing edge sealant for insulating glass units. The sealant contains a thermoplastic hot melt resin and an atmospheric curing resin of the type which polymerizes upon exposure to an ambient atmosphere. The atmospheric curing resin is combined with the thermoplastic hot melt resin as a single material. The sealant is described as comprising 10-90% by weight of a thermoplastic hot melt resin comprising a solid chlorinated paraffin and 5-50% by weight of an atmospheric curing resin such as a silane-terminated polyurethane.